The present invention relates to Langmuir-Blodgett thin film made of organic material having dye skeletons, and also to an organic thin film element having the Langmuir-Blodgett thin film.
Researches have been conducted in many places on various devices having elements having organic thin films, a typical example of which is Langmuir-Blodgett thin film. Such devices are disclosed in, for example, Japanese Patent Disclosure No. 52-35587, Japanese Patent Disclosure No. 55-17505, Japanese Patent Disclosure No. 57-196143, Patent Disclosure No. 60-239739, Japanese Patent Disclosure No. 61-37891.
The inventors hereof have invented organic thin film elements containing donor molecules or acceptor molecules, and methods of manufacturing these elements, these elements and methods are disclosed in Japanese Patent Disclosure No. 62-65477, Japanese Patent Disclosure No. 62-76551, etc. These elements use LB film containing dye molecules.
A number of reports have been published which relate to LB film containing dye skeletons. Dye alone can scarcely form a thin film. It is difficult to form uniform film since the dye skeletons firmly associate with each other and have great cohesion. Due to the great cohesion of the dye skeletons, film made of these skeletons will undergo three-dimensional crystallization, or will have excessive viscosity, even if it is developed on the surface of water.
Cohesion of the dye skeletons can be reduced by introducing bulky hydrophobic radicals into the dye skeletons. When the dye skeletons have their mutual cohesion thus reduced, stable monomolecular film can be formed on the surface of water with high efficiency. To provide material having dye skeletons having small mutual cohesion, dye molecules have been synthesized, each having one long alkyl group. In most cases, however, these dye molecules cannot form, by themselves, stable monomolecular films, failing to provide uniform LB films on the surface of water.
Generally, a long chain aliphatic acid is mixed with dye molecules, thereby forming a stable monomolecular film. This method inevitably reduces the concentration of the dye. Nor does it guarantee a uniform mixing of the dye molecules and the long chain aliphatic acid. To make matters worse, it is impossible with this method to strictly control the structure of the film to be manufactured.
Hitherto, dye molecules and matrix molecules of long chain aliphatic acids such as arachidic acid are mixed, and LB films are formed of the resultant mixture on a substrate. It is generally difficult to mix two kinds of molecules thoroughly. In some cases, the molecules of the first kind form a domain, and the molecules of the second kind form another domain, either domain being tens to hundreds of micrometers in size. This tendency is pointed out in H. Moehwald, "Thin Solid Films," Vol. 159, p. 1, 1988. Such domains, if formed, are not so much problematic, provided that the elements made having such LB film are relatively large. They give rise to a great problem, however, to the desired high integration density of electronic devices.
The condition in which the components of such LB film changes with time in some cases, as is discussed by Hamaguchi, Nishiyama, Fujihira in their report published by Electrochemical Society of Japan, 1986, p. 76, D123. The changes in the mixing condition may result in the instability of operating characteristics of the elements using the LB film.
Various kinds of dye molecules have been synthesized which have dye skeletons, each having two long alkyl groups. Of these kinds of dye molecules, many can form, by themselves, stable monomolecular films on the surface of water, as is disclosed in Nakahara, Fukuda, and Satoh, "Thin Solid Films," Vol. 133, 1985, p 1. In many cases, however, it is difficult to introduce two long alkyl groups to a dye skeleton, by the existing chemical synthesis techniques. A dye molecule having a dye skeleton and two alkyl groups linked to the skeleton by means of ester linkages which is readily hydrolyzable is known (e.g., a dye molecule having a dye skeleton and phospho-lipids bonded to the skeleton). In some cases, hydrolyzable linkage may be cleaved in the process of synthesizing dye skeletons, or in the process of coupling long alkyl groups to the dye skeletons.
Dye molecules which can function as acceptors cannot be so easily synthesized as dye molecules which can function as donors. It is difficult to control the degree to which these dye molecules can function as acceptors.